Display panel or portion thereof with a transitional graphical user interface



FIG. 1 is a front view of a display panel or portion thereof with agraphical user interface showing the first image in a sequence; and,

FIG. 2 is a front view of the second image thereof.

The appearance of the image transitions sequentially between the imagesshown in FIGS. 1-2. The process or period in which an image transitionsto another forms no part of the claimed design.

The broken line showing of the display panel or portion thereof forms nopart of the claimed design.

CLAIM The ornamental design for a display panel or portion thereof witha transitional graphical user interface, as shown and described.